Rest is definitely important, you have to listen to your body. If it's feeling really rough, it might be good to take a few days rest. My weekends are all about that, I take of Saturday and Sunday to refuel and rest.
Today my legs were destroyed from yesterday, so I was thinking that my run would suffer. But I started taking Superpump 250 to help me to get more out of my workouts on chest and arms... and the run was helped a lot too. I felt like I could have ran 4 miles! It was amazing, I felt no pain at all. I did watch my heart rate though, just to be cautious.
I also was able to bench 130 instead of my normal 100, which was a nice surprise. But since today was my start day and I was at a half dose and not the full dose, the boost ran out before I finished my workout.